A computer has a coupling port for coupling devices such as a memory device, an arithmetic device, an output device. In a case of coupling a plurality of these coupling devices, an expansion device on which a plurality of coupling ports are mounted is used. For example, the expansion device functions as a coupling control device that couples the coupling devices coupled to a selected coupling port and the computer.
As an example, in a storage device, an expansion device called an expander (EXP) is used for coupling a plurality of memory devices such as a plurality of hard disk drives (HDD) and redundant arrays of inexpensive disks (RAID) devices.
The EXP has a plurality of physical ports (PHY) as the coupling ports. The PHY has a serial parallel conversion circuit such as a serializer/deserializer (SerDes). The EXP couples the memory devices that are access destinations and a controller module (CM) which controls the input and output to and from the memory device by switching a path between the CM and the PHY.
As described above, in a case where the computer and the coupling devices are coupled via the expansion device, and when an error occurs at the time of access to the coupling devices, a work for specifying whether a source of error is the expansion device or the coupling device is performed.
In a case of the storage device described above, as a method of specifying the source of error, a loopback diagnosis is used, in which a data frame is transmitted from the CM to the memory device that is the access destination, and then, the source of error is specified referring to the response to the data frame. In addition, a diagnosis method is proposed, in which a connection frame (a frame used for establishing connections between devices) is transmitted to the device from which the fault is detected by the loopback diagnosis and fault information included in the response to the connection frame is investigated. Japanese National Publication of International Patent Application No. 2013-515981 is a sample of the background art literature.